The present invention relates to an attachment to a sewing machine for cutting the edges of material comprising a fixed blade and a movable blade drivable by the needle bar of the machine.
Attachments to sewing machines for cutting the edges of sewing material moving toward the sewing site, are known in various versions. Ordinarily, the blade which is driven by the needle bar and moves essentially in a vertical direction cooperates with a counter blade fixedly connected to a part of the machine. In this connection, the movable blade is either directly mounted to the needle bar or is arranged on a blade holder fastened on the working surface of the machine, as illustrated, for example, in Italian Pat. No. 603,617. The fixed counter blade is either a correspondingly constructed edge of the needle plate or a cutting edge mounted thereto.
The conventional attachments are cumbersome in handling. Mounting and adjusting operations are required with each use. Thus, it is necessary, for example to exchange the needle plate, and the blade holder must be attached on the working surface. To obtain a clean cut, an exact adjustment of the two blades with respect to each other is then necessary in each instance.
To avoid these disadvantages, the present invention has the purpose of providing an attachment of the aforementioned type which can be mounted as a unit by a few simple manipulations and requires no adjustment whatever. For this purpose, the attachment of the present invention is characterized by a holder for the fixed blade, which is detachably affixed to the presser bar of the sewing machine and is provided with a foot plate and a presser sole articulated thereto in a pendulating fashion, whereby the movable blade articulated to the holder is in driving connection with the needle bar by way of an articulated lever mechanism supported at the holder. The lever connection between the needle bar and the movable blade is advantageously such that the movable blade during the downward stroke of the needle bar is pivoted about a horizontal axis lying above the cutting edge of the fixed blade and, in the advancement direction of the length of material, behind the point of engagement of the two blade edges, this pivoting being done in the cutting sense, but only at the point when the needle bar has reached the central position corresponding to the entrace of the needle into the length of material, or has exceeded such position. In the case of sewing machines equipped for zigzag sewing, the arrangement is such that the lateral distance of the cutting plane from the center of the stitching width of the machine is at most equal to or somewhat smaller than one-half the stitch width, wherein the movable blade is recessed in the stitching zone of the needle in such a way that the needle can penetrate within or outside of the blade plane, thus making it possible to sew around the cutting edge of the length of material to prevent raveling. However, an important feature is the installation of all of its parts at a common holder, forming a unit, whereby the device can be affixed to the presser bar of the sewing machine in place of a customary presser foot and is ready for operation without previous adjusting or assembly work. Since the drive derivation from the needle bar for the movable blade is suitably effected by means of a forked lever engaging a dog at the needle mount, the fixation of the device to the presser bar and the drive connection of the device with the needle bar can be executed in the same operating step without any problems.